1. Field of the Invention
The present invention relates to a diagnostic X-ray apparatus for emitting X-ray pulses for examining an object and including a solid-state image sensing device for providing an image signal for display of an X-ray radiographic image.
2. Description of the Related Art
In a known diagnostic X-ray apparatus, an X-ray directed from an X-ray tube toward an object under examination and transmitted through the object is converted into an optical image by an image intensifier (I.I.). This optical image is picked up by a TV camera, and is converted into an image signal for display as a fluoroscopic image on a monitor. The image signal is converted into a digital form by an A/D converter, and various kinds of image processing are performed, as needed.
In a conventional TV camera, an interlaced scanning system is employed to respectively scan odd- and even-numbered horizontal scanning lines in odd-and even-numbered fields. In recent years, a solid-stage imaging device such as a charge-coupled device (CCD) is often used as the TV camera. The type of solid-state imaging device is divided into a field storage mode and a frame storage mode with regard to a storing mode of signal charges.
In the field storage mode, each pixel stores signal charges during only a field period. Two pixels adjacent to each other in the vertical direction are read as one pixel, and these two pixels are shifted upward or downward by one pixel in the odd-or even-numbered field. More specifically, two horizontal scanning lines of the imaging device are used as one horizontal scanning line of a TV signal in the field storage mode.
In the frame storage mode, each pixel stores signal charges during a frame period. The charges of the pixels of the odd-numbered horizontal scanning lines are read in the odd-numbered fields, and the charges of the pixels of the even-numbered horizontal scanning lines are read in the even-numbered fields. More specifically, each horizontal scanning line of the imaging device is used as the corresponding horizontal scanning line of a TV signal.
For a diagnostic X-ray apparatus including a CCD performing interlaced scanning in a field storage mode, an X-ray pulse having a predetermined pulse width is emitted from the X-ray tube and a pulse width of the X-ray pulse emitted from the X-ray tube is one-half of the predetermined pulse width when a field shift pulse is generated by a pulse generator. The predetermined pulse width is decided according to a preliminary X-ray emission.
For a diagnostic X-ray apparatus including a CCD performing interlaced scanning in a frame storage mode, the X-ray pulse having the predetermined pulse width is emitted from the X-ray tube and a series of video signals is generated by the CCD at the timing shown in FIG. 1 or FIG. 2. The predetermined pulse width is decided according to a preliminary X-ray emission.
In FIG. 1, the X-ray pulse is emitted from the X-ray tube in the first field period of the first frame period and each pixel of the CCD stores signal charges corresponding to this X-ray pulse emission. The charges of the pixels on the even-numbered horizontal scanning lines are read in the second field of the first frame, and the charges of the pixels of the odd-numbered horizontal scanning lines are read in the first field of the second frame.
In FIG. 2, the X-ray pulse is emitted from the X-ray tube in the second field period of the first frame period and each pixel of the CCD stores signal charge corresponding to this X-ray pulse emission. The charges of the pixels on the odd-numbered horizontal scanning lines are read in the first field of the second frame, and the charges of the pixels of the even-numbered horizontal scanning lines are read in the second field of the second frame.
With reference also to FIG. 3, the charges of the pixels on the odd-numbered horizontal scanning lines are read in the first field of each frame and the charges of the pixels on the even-numbered horizontal scanning lines are read in the second field of each frame.
Thus, in the case as shown in FIG. 1, the first output field image signal is the even field image signal, and in the case as shown in FIG. 2, the first output field image signal is the odd field image signal. For example, when the image signal is stored in a frame memory, it is possible that the exact frame image signal is not provided. This is because the field image signal provided to the frame memory first is stored at a predetermined region of the frame memory.